By Linda Conlin, Pro to Pro Managing Editor

Most of us enjoy the outdoors in warm weather, but mosquitos surely can take the fun out of it. Repellant sprays and candles do a fair job of keeping those nasty creatures away, but there’s a way to boost their efficacy without adding to the smell. New research led by scientists at the University of Washington, published in Nature Communications, indicates that a common mosquito species, after detecting a gas that we exhale, flies toward specific colors, while ignoring others.

It’s known that mosquitos are attracted to human breath, sweat, and warmer skin temperatures, but now color can be added to the list. Everyone’s skin, regardless of pigmentation, gives off a long-wavelength signal in the red-orange range (>600 nm). Researchers showed that the mosquitos’ sense of smell, or olfaction, triggers a response to visual cues in the longer wavelengths -  red, orange, (wavelength 600-650) black, (absorbs heat) and cyan (wavelength between 490-520 nm). Although the mosquito’s response to certain wavelengths requires more study, when the mosquitos smelled CO₂, as from our breath, they were attracted to those colors, but not to others.

For the experiments, researchers tracked more than 1.3 million mosquito trajectories. Mosquitos were placed in a chamber with a variety of visual stimuli, such as a colored dot. When there were no odors in the chamber, the mosquitos ignored the stimuli. However, when CO₂ was sprayed into the chamber, they flew toward red, orange, black, and cyan, but ignored green, blue, or purple. Part of the study introduced a researcher’s hand into the chamber, (all in the name of science) and that, too, was ignored until CO₂ was present. The odor/color connection was explored further. Genetically modified mosquitos that could not smell CO₂ showed no color preference, and others modified to be unable to detect longer light wavelengths showed a similar lack of preference. 

Mosquitos’ preferences for color were studied in the early twentieth century, leading to clothing in khaki and light blue for the military and outdoor enthusiasts. This research shows, however, that it isn’t color alone, but the combination of color and odor that ring the dinner bell for mosquitos. Researchers believe that the CO₂ in our breath triggers a visual response to wavelengths in the same range as human skin, but more study is needed. So while holding your breath isn’t an option to avoid mosquitos, try a different wardrobe, stay cool, and try not to sweat.

Learn how color signals are redefined with selective filtering of specific wavelengths of light with our CE, Wiley X Lens Technology Redefining Color with Captivate, at 2020mag.com/ce.